In wireless communications systems, such as satellite communication systems, data can be communicated from one location to another via a wireless relay. For example, in a satellite communications system, data can be communicated between gateways and user terminals via a satellite. It is generally desirable to increase capacity of the communications system. Some approaches for increasing capacity involve increasing power, but such approaches can have various limitations. For example, power increases can be limited by power budgets (e.g., practical power limitations of system components, etc.) and/or by regulatory constraints (e.g., maximum allowed transmission power, etc.), and increases in power can have a disproportionately small impact on capacity (e.g., following a logarithmic gain when operating near the Shannon limit). Some other approaches involve increasing bandwidth (e.g., via greater frequency reuse, since spectrum allocations are typically fixed and limited). However, increasing bandwidth reuse typically involves increasing the number of beams servicing ground terminals and decreasing beam sizes. Decreased beam sizes present a number of challenges, such as increased size, weight, complexity, cost, etc. of the satellite and/or ground terminals; increased accuracy required for antenna pointing and attitude control in the satellite; etc. Small beam sizes also present challenges with respect to matching the provided system capacity (e.g., providing an equal share to each of the beams) to demand (often very unevenly distributed over the user coverage area).
Some of these concerns can be addressed for certain applications using techniques such as on-board beamforming arrays and hardware, but such techniques can further increase the size, weight, cost, and complexity of the satellite. One approach to reducing the complexity on board the satellite, while maintaining certain features of on-board beamforming, is to shift the complexity to the ground. So-called “ground-based beamforming” (GBBF) approaches can be effective, but implementations have tended to focus on lower bandwidth contexts (e.g., providing a few MHz of user link bandwidth for L-band carrier frequencies). Conventional GBBF has a feeder bandwidth expansion problem, as the required feeder link bandwidth is a multiple of the user link bandwidth, the multiplication factor being related to the number of antenna elements provided by the user link array. So for example, to provide 1 GHz of user bandwidth (e.g., at Ka-band) with a 100-element user-link beamforming array may require 100 GHz of feeder link bandwidth. The bandwidth expansion problem can frustrate practical application of conventional GBBF to high-capacity satellite systems.